OS 10.4 - Tiger or Leopard for G4 emac?

I got an ipod nano the other day but my emac is still on panther (10.3.9) so I need to upgrade to either tiger or leopard. The apple store 'genius' says that I can't run leopard and I can't find tiger for sale anywhere other than ebay (where I don't want to buy from).

Any suggestions of where to get tiger in the UK or if I can run leopard - my emac is a G4 1GHz PowerPc with768mb SDRam.

mac: a waterproof raincoat made of rubberized fabric
MAC: a data communication protocol sub-layer, also known as the Media Access Control
Mac: a brand name which covers several lines of personal computers designed, developed, and marketed by Apple Inc.